Mechanistic insights of efficient aromatic organic compounds oxidation using biochar derived from coking wastewater sludge

Coking wastewater sludge possessed potential environmental hazards and pyrolysis was a desirable approach which could converted it into one functional carbonous material. The sludge-based biochar (SC-N3) originated from the feedstock of sludge from the regenerated water treatment had various iron-containing species and exhibited the effective catalytic ability. Compared with the degradation of the four pollutants (i.e., phenol, pyridine, quinoline and indole) alone, the mixed of the four pollutants in simulated coking wastewater exhibited a prominent different degradation trend, where the removal rates of indole and quinoline were enhanced from 45% and 30% to 98.9% and 82.3%, respectively. The quinone intermediates from phenol degradation, played a critical role in enhancing the removal rates of indole and quinoline as the electron transfer medium. Both the free radical pathway dominated by •OH and non-radical pathway with 1O2 play the main role in indole degradation, while •OH was the main factor in the catalytic degradation of phenol, quinoline and pyridine. By analysis the intermediates elucidated by Fourier transform ion cyclotron resonance mass spectrometry and three-dimensional excitation-emission matrix fluorescence spectra, the degradation molecular characteristics and pathways of the four pollutants in simulated coking wastewater were deciphered. The findings indicated that the catalyst SC-N3 prepared from the coking wastewater sludge presented unique catalytic properties and possessed a promising application in the degradation of refractory wastewater.